A flow rate sensor for determining the air mass taken in by an internal combustion engine having two heating resistors and two reference temperature sensors is discussed in European Published Patent Application No. 0 955 524. Prior to the air flowing over the heating resistors, the temperature of the air flowing past the flow rate sensor is detected by the reference temperature sensors. Both heating resistors are used for measuring the air mass flowing over the flow rate sensor. The effect of the first heating resistor in the flow direction heating the air flowing over it is utilized here, which results in the second heating resistor in the flow direction needing less heating energy than the first heating resistor to reach a predefined temperature. The cooling of the first heating resistor in the flow direction results in reduced electrical resistance of this heating resistor, while the second heating resistor is only slightly cooled by the air heated by the first heating resistor, so that the electrical resistance of the second heating resistor, under what are otherwise the same starting conditions, is greater than the electrical resistance of the first heating resistor. From the difference of the temperature-dependent resistances of the first heating resistor and the second heating resistor or from the difference of the necessary for maintaining constant (excess) temperatures, conclusions are drawn with regard to the air mass flowing past the flow rate sensor.
It is further known that a temperature sensor may be assigned to each heating resistor to be used for measuring the temperature of the heating resistor.
This circuit system is thus made up of two heating resistors, two temperature sensors, and two reference temperature sensors having a total of 2 times 6=12 terminals. If these 12 terminals are to be accommodated on a chip, the size of the chip, among other things, is predetermined by the number of terminals. The costs of a chip, among other things, also depend on its size.